As semiconductor devices have been highly integrated, the dimensions of the semiconductor devices on a substrate have been reduced. For example, the area of a gate structure of a transistor has been reduced, which may result in short channel length around the gate structure. Thus, methods of increasing the channel length without increasing the size of the device have been studied.
As a result, methods of forming a recessed channel transistor in which a lower portion of a gate structure may be buried in a substrate have been introduced. The above gate structure may be called a recessed gate structure. The recessed channel transistor may have increased channel length, however, an overlapping area of the recessed gate structure with a drain region may increase, so that, the gate induced drain leakage (GIDL) of the recessed channel transistor may be increased. Thus, dynamic random access memory (DRAM) devices having the recessed channel transistor may have poor refresh characteristics.